A computer's power supply, as the name suggests, provides power to the computer. The power supply consists of a wire (or wires) connecting to a power source (generally an outlet), a wire (or wires) connecting to the computer, and a power brick.


Here is a desktop power supply, which will generally be placed within the computer.

It would certainly be convenient for there to be just one wire connecting the computer to the power source, but the power brick is necessary to convert the energy coming from the power source into a form of energy that can be used by the computer. This issue stems back over a century, to when the energy grid was being built. There were two types of electricity that could have been used, one with alternating current, meaning that the direction the electricity flows in alternate directions, and one with direct current, meaning that the electricity flows in the same direction. Alternating current was chosen because it was easier to transport over long distances, and better suited the devices of the time that required energy, such as refrigerators. However, today, we have a great number of electronics powered by semiconductors (mainly silicon), which can only use direct current. Because of this, a power brick is needed for all of the devices, which converts the AC electricity coming from the power source into DC electricity, which can then be sent to the computer. Unfortunately, during this process, a portion of the energy is lost (which is the reason that a power brick will often heat up when in use), though nothing can be done to change this as the entire power grid is based off of alternating current.


An illustration of the flow of direct and alternating current.

Different computers need different amounts of power, and therefore the power supplies of these computers have different energy outputs. Small laptops may only need a few volts of power, while supercomputers may have multiple powers supplies of many hundred of volts. Some of the first modern computer power supplys were created by IBM in the 1980's, and the design has not been changed much since. Computers have the ability to run off different amounts of power (especially those that are self-built). Although many assume that the best power supply is the most powerful, a more important aspect is efficiency. Even if a power supply has a very high voltage, that number is insignificant if the unit is inefficient, as only a fraction of the power will make it to the computer. A good standard for a power supply's efficiency is "80 plus", meaning that, in the conversion of AC electricity to DC electricity, at least 80% of the power is transferred to the computer, with the other <20% being lost as heat.


This is a diagram of the process through which a power supply converts AC electricity to DC electricity..

A power supply unit's placement generally depends on the type of computer in question. For desktops, the power supply will generally be inside the computer, while in laptops it is usually part of a detachable cord. Other computing devices, such as phones and tablets, have the same set up as laptops. Portable devices also have an internal battery (usually lithium-ion) that powers them. This means that the power supply isn't necessarily channeled directly to powering the computer, as it is stored as energy within the battery and then sent from the battery to the computer. For desktops, there is no battery and the power is sent directly, which is why a desktop will immediately shut off when it is disconnected from the power source.

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  1. Chiappetta, Marco. "How to Pick the Best PC Power Supply." PCWorld. PCWorld, 04 Feb. 2013. Web. 22 Nov. 2016. <>.
  2. "Direct Current Versus Alternating Current." HowStuffWorks., n.d. Web. 22 Nov. 2016. <>.
  3. Fischer, Tim. "What Is a Power Supply Unit?" Lifewire. N.p., n.d. Web. 22 Nov. 2016. <>.